The present invention relates to video data processing, and more particularly to a video discriminator for automatically determining the line rate of an input video signal and generating an appropriate format select signal.
Analog video that is applied to the input of a digital video processor may be in either the PAL or NTSC formats which have different line rates. The
line rate is 625 lines per frame, or 312.5 lines per field, and the NTSC line rate is 525 lines per frame, or 263.5 lines per field. As illustrated in FIGS. 1 and 2 the NTSC format has twenty lines of vertical blanking between fields, which includes a vertical interval signal. Likewise the PAL format has twenty-five lines between fields. During the vertical interval a plurality of sync pulses occur at twice the horizontal sync rate. Vertical sync is defined within the vertical interval by a plurality of wide sync pulses occurring in succession, six for the NTSC format and five for the PAL format.
Typically a television studio or production house would have separate equipment to process the different video formats. Currently with the establishment of various digital television video standards, such as the CCIR-601 and RP125 standards, video signals are converted to on of these digital standards for processing. The advent of more sophisticated digital video processors allows both formats to be input to the digital video processor so that video of both formats may be combined into a single output. However in order to switch between the input formats manual techniques, such as manual jumpers, switches and the like, are used to convert the equipment from one format processing to the other.
What is desired is a means for automatically discriminating between the two video formats so that a video processor can readily switch between the two formats without manual intervention.